Yu. A. Antonov

Phase state of aqueous gelatin–polysaccharide (1)–polysaccharide (2) systems

Optical microscopy, ultracentrifugation, phase analysis and turbidimetric titration methods were used to study phase state and phase equilibria of quaternary water-gelatin-pectin-dextran system in the absence of salts and at pH higher than the isoionic point. It was found that these systems are two-phase ones, contrary to the single-phase behaviour of the ternary water-gelatin-pectin and water-gelatin-dextran systems under the same conditions. The observed phase separation is the result of incompatibility of gelatin with pectin, dextran molecules being distributed practically uniformly between coexisting phases. This phenomenon is rather typical for many water-gelatin-polysaccharide-1-polysaccharide-2 systems under the conditions when all the pairs of biopolymers are compatible. The high compatibility of gelatin with pectin or dextran in the ternary systems under given conditions is due to the formation of weakly bonded interpolymer complexes. The incompatibility of gelatin with pectin in the presence of dextran can be explained by the blockage of the reactive gelatin groups due to their competitive interactions with dextran.

Interactions and compatibility of ribuloso-1,5-bisphosphate carboxylase/oxygenase from alfalfa with pectin in aqueous medium.

HPLC, dynamic light scattering, CD- and fluorescent spectroscopy, and phase analysis methods are used to study the effect of Coulomb and non-Coulomb interactions between alfalfa rubisco and pectin on their thermodynamic compatibility. In the acid region of pH, water insoluble interpolymer complexes stabilized by both the Coulomb and non-Coulomb bonds are formed. In the neutral and alkaline regions, the complexes soluble in water are formed via non-Coulomb bonds, due to both the hydrophobic interaction involving the ester groups of pectin and the hydrogen bonding between dissimilar molecules. The compatibility of these biopolymers is sensitive to the esterification degree of pectin. With the latter increasing, compatability increases at neutral pH, but decreases considerably in the acidic region.

A Study of cryostructuring of polymer systems. 41. Complex and composite poly(vinyl alcohol) cryogels containing soluble and insoluble forms of chitosan, respectively

Complex macroporous poly(vinyl alcohol) (PVA) cryogels have been obtained by cryogenic treatment (freezing at–20°C for 12 h followed by defrosting at a rate of 0.03°C/min) of PVA–chitosan hydrochloride mixed solutions. The subsequent alkaline treatment of the cryogels has resulted in the transformation of the water-soluble salt form of chitosan into its insoluble basic form, which coagulates inside the bulk of the continuous phase of PVA cryogel into small particles with sizes of 2–5 µm. In the resulting composite cryogels, these particles play the role of an “active” filler, which increases the rigidity and heat endurance of the gel material. It has been shown that the sorption capacity of such chitosan particles entrapped into the bulk of composite cryogels with respect of bivalent copper ions is noticeably higher than the sorption capacity of ground chitosan particles incorporated as a discrete filler into the continuous phase PVA cryogels. The study of the properties of PVA–chitosan hydrochloride mixed solutions revealed that these polymers are, to a large extent, compatible with one another in a common solvent at a low ionic strength. Therefore, liquidliquid phase separation of these systems due to the thermodynamic incompatibility of macromolecules of different natures is observed only upon increasing the ionic strength by adding a low-molecular-mass salt (NaCl, 0.15 mol/L) to the solution.

Use of membraneless osmosis for concentration of proteins from molecular-dispersed and colloidal-dispersed solutions (review)

Theoretical principles, practical realizations, and future trends in the use of the method of protein concentration based on thermodynamic incompatibility of proteins with polysaccharides are reviewed. The relationship between structural features of these biopolymers (molecular weight, rigidity, and conformation of the polysaccharide chain; the nature and ionogenic properties of its functional groups; the type of protein and state of its molecules), as well as major physicochemical parameters (pH, ionic strength, and temperature) and mechanical shift energy of the system, on the one hand, and its phase diagram, on the other hand, are discussed.

A study of cryostructuring of polymer systems. 43. Characteristics of microstructure of chitosan-containing complex and composite poly(vinyl alcohol) cryogels

The microstructure of complex and composite poly(vinyl alcohol) (PVA) cryogels containing water-soluble chitosan hydrochloride (ChHC) of dispersed particles of water-insoluble chitosan base (Ch), respectively, has been studied by optical microscopy and attenuated total reflection FTIR spectroscopy. The macroporous morphology of cryogels has been studied using preparations in the form of thin (~10 μm) sections and discs 1 mm thick. The introduction of non-gelling additives (NaCl and ChHC) into an initial PVA solution causes significant changes in the size and shapes of macropores in the complex cryogels formed by freezing–defrosting, as compared with the pores in the samples obtained under the same conditions without additives. The reasons for the changes are the process of phase segregation and the influence of low- and high-molecular-weight electrolytes on crystallization of ice, which plays the role of a porogen upon cryotropic gelation of aqueous PVA solutions. As a result of an alkaline treatment of the complex cryogels, which transforms ChHC into Ch, microcoagulation of chitosan yields discrete, almost spherical, particles with sizes of about 1–5 μm. IR spectral studies have shown that concentration gradients of the gelling and nongelling polymers arise along the thickness of the gel discs, with PVA concentration prevailing near the lower surface and ChHC or Ch concentration dominating near the upper surface of the disc.